Chemical States Regulation and Performance on Selective Catalytic Reduction of NOx with NH3 at Low-Temperature over CuOx/SiO2 Catalysts
Selective catalytic reduction(SCR)technology is the primary approach to achieving ultra-low emissions of nitrogen oxides(NOx),using NH3 as a reducing agent to convert NOx into N2 and H2O.However,the existing V2O5-WO3(MoO3)/TiO2 catalysts generally works at high-temperatures typically ranging from 300 to 420 ℃,which fails to meet the requirement at low-temperature(100～200 ℃)for numerous non-coal power industries.The development of novel catalysts meeting the deNOx at low-temperature have significant energy consumption and cost advantages due to being free from the reheating of flue gas.In this study,CuOx/SiO2 catalysts were prepared using the sol-gel method,with the calcination atmosphere controlling to 50％O2(volume fraction),standard N2,0.1％NH3(volume fraction),0.4％NHx(volume fraction),and 1.0％NH3(volume fraction),resulting in samples denoted as CuOx/SiO2-O,CuOx/SiO2-N,CuOx/SiO2-0.1A,CuOx/SiO2-0.4A and CuOx/SiO2-1.0A,respectively.The phase composition was analyzed using X-ray diffraction(XRD),the morphology was observed through scanning electron microscopy(SEM),the specific surface area and pore structures were analyzed using a fully automated surface area and porosity analyzer(Micromeritics APSP 2460)via N2 adsorption-desorption tests,the surface elemental chemical states were analyzed using X-ray photoelectron spectroscopy(XPS),and the temperature-programmed desorption(NH3-TPD)and temperature-programmed reduction(H2-TPR)tests were conducted using a fully automated temperature-programmed chemisorption analyzer(Micromeritics Autochem Ⅱ 2920).XRD results indicated that the catalysts were primarily composed of amorphous structures,with the presence of Cu2O in CuOx/SiO2-1.0A,CuOx/SiO2-0.4A,CuOx/SiO2-0.1A and CuOx/SiO2-N catalysts,evidenced by gradually decreasing diffraction peak intensities of Cu2O.Notably,CuOx/SiO2-O catalyst calcined in 50％O2(volume fraction)atmosphere exhibited no Cu2O diffraction peak.This suggested that with an increased reducing ability in the calcination atmosphere,it was promoted of the formation of Cu2O phase in CuOx/SiO2 catalysts.This was further confirmed by H2-TPR tests,where the reducing ability of the calcination atmosphere led to a reduction in H2 consumption,indicating an increased Cu2O phase.These catalysts exhibited a mesoporous structure,including both open and partially blocked mesopores.A comparison of the Brunauer-Emmett-Teller(BET)surface area and Barret-Joyner-Halenda(BJH)pore volume and average pore diameter of CuOx/SiO2 catalysts revealed a gradual decrease with increasing reducing ability of the calcination atmosphere.XPS analysis demonstrated that with an enhanced reducing ability in the calcination atmosphere,the surface Cu2O component content increased,the proportion of Cu+increased,and Cu2+/Cu ratio decreased.These findings indicated that the calcination atmosphere significantly influenced the phase,structure and chemical states of CuOx/SiO2 catalysts,further impacting their catalytic efficiency.The catalytic performance of CuOx/SiO2 catalysts for NO reduction was evaluated within the temperature range of 100～200 ℃.The results showed that CuOx/SiO2-O catalyst exhibited higher activity in the low-temperature range of 100～125 ℃,while CuOx/SiO2-1.0A catalyst exhibited higher activity in the high-temperature range of 150～200 ℃.CuOx/SiO2-O catalyst had a higher surface Cu2+content which played a major role in the low-temperature range,while CuOx/SiO2-1.0A catalyst had a higher surface Cu+content which played a major role in the high-temperature range.The coexistence of Cu2+and Cu+components in the catalysts contributed to their synergistic catalytic activity.In summary,CuOx/SiO2 catalysts revealed excellent performance of deNOx at low-temperature.The adjustment of the calcination atmosphere could control the physicochemical properties of the catalysts,thereby influencing their catalytic activity.The findings of this study provided valuable insights for the development of efficient low-temperature deNOx catalysts for the ultra-emission of flue gases.
deNOx at low-temperatureselective catalytic reduction(SCR)Cu-based catalystchemical stateredox
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